Accurate vehicle navigation

ABSTRACT

Method and system for accurate vehicle navigation and tracking within a selected lane on a roadway or a waterway. A location determination (LD) receiver, carried on the vehicle, receives LD signals from satellite-based LD signal sources, receives LD signal correction information from one or more other wide area LD correction sources, estimates a corrected vehicle location (good to within 10-50 cm) and velocity (optional) relative to one or more lane boundaries that define the selected lane, and displays vehicle location and velocity within the lane. When the vehicle approaches a lane boundary too quickly, or is too close to the lane boundary, an alarm signal or other control mechanism can be activated. The LD correction information is delivered to the LD receiver via a channel of suitable bandwidth. The system can also be used to map and store lane boundary coordinates for selected segments of a roadway or waterway.

FIELD OF THE INVENTION

This invention relates to accurate determination of location of avehicle on a roadway or a waterway relative to a lane boundary.

BACKGROUND OF THE INVENTION

Satellite-based signal sources, such as the Global Positioning System(GPS) or Global Orbiting Navigational Satellite System (GLONASS) or LowEarth Orbit (LEO), for location determination (LD) can now providecorrected signals with relatively small associated inaccuracy.Previously, a vehicle navigation system might provide a map of a localregion, including major roads, and provide an approximate graphicalindication of the present location of a vehicle relative to the roadsystem shown on the map. However, it is also of interest to provide amore detailed image showing the vehicle relative to a particular roadwayor waterway on which the vehicle is presently located. Here, theassociated inaccuracy should be no more than 50 cm, in order that thevehicle be accurately located relative to a particular lane in which thevehicle travels. It would not be sufficient here to merely estimate thevehicle and to provide a snap-to-grid operation that places the vehiclein the roadway or waterway lane that is nearest to the vehicle presentlocation. This is especially true if the LD system is to provideautomatic guidance within a roadway lane. If the vehicle “wanders” toofar afield, the vehicle may collide with a vehicle in an adjacent lanethat is moving in the same direction or in an opposite direction.

Another problem that arises here is communication to the vehicle oflocation correction information and related data that allows an on-boardsignal processor to determine the vehicle location with sufficientaccuracy. Many vehicle communication systems available today only allowtransmission of a few hundred bits of relevant information per second.This rather low rate of (correction) information transmission would notpermit LD computations and corrections to be made at a rate (one or moretimes per second or more for each of three or more LD signals received)that is required for automated roadway or waterway guidance. A real timekinematic (RTK) system allows correction of LD signals, such as GPSsignals, using LD correction signal sources that are spaced apart fromthe user by a distance that is usually no more than about 40 km, whichstrongly limits the region over which a vehicle can operate with one ora few RTK reference stations.

What is needed is a wide area LD correction system that estimates andprovides corrected vehicle location up to several times per second, withan inaccuracy of no more than 10-50 cm within a selected roadway orwaterway lane, and that indicates when the vehicle is too close to, andmoving toward, a lane boundary. Preferably, the system should operateover a wide area, such as a region with diameter between 50 km and 5000km. Preferably, the system should also determine a velocity at which thevehicle moves toward a nearest lane boundary. Preferably, the systemshould also allow accurate mapping of lane boundaries for a roadway orwaterway.

SUMMARY OF THE INVENTION

These needs are met by the invention, which provides a Wide Arealocation information transmission and processing system that permitscommunication of location correction data for each of several LD signalsources and that permits computation of corrected location coordinatesof a vehicle and graphical, alphanumeric or other display of vehiclelocation relative to a chosen roadway lane, with an associatedinaccuracy of at most 10-50 cm and at a rate of several times persecond. An LD correction system, such as DGPS or WAAS for the GPS,determines local corrections for pseudoranges or related measurementsfor visible LD signal sources (satellites) and uses a wirelesstransmission system, such as SDARS or FM subcarrier or Sky Station orPrivate Radio, with modest information transfer rate to deliver the LDcorrection information to an LD signal antenna and LD receiver carriedon a subscriber vehicle. The vehicle LD receiver receives LD signals,corrects the LD signals using the LD correction information, computesthe present location and (optionally) velocity of the vehicle relativeto a selected roadway or waterway lane on which the vehicle travels.Optionally, the LD receiver provides an alarm signal if the vehicle isapproaching a lane boundary too quickly or is too close to a laneboundary. A Wide Area LD correction system can also be used to mapboundaries for vehicle travel lanes to provide a database of boundarylane descriptions that can be subsequently used for Wide Area vehicletracking within a travel lane.

As used herein a “Wide Area” LD correction system is an LD correctionsystem with at least three sources of LD correction signals that arespaced at least a selected distance d1 apart, where a distance d2between any location and each of at least two of these LD correctionsignal sources is greater than about 0.5 d1. The distance d1 may bechosen to be a suitably large value, such as 50 km, 100 km, 500 km or1000 km.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3 and 5 illustrate embodiments of the invention.

FIG. 4 illustrates lane boundary crossing by a vehicle.

FIG. 6 illustrates apparatus for practicing the invention.

DESCRIPTION OF BEST MODES OF THE INVENTION

FIG. 1 illustrates practice of one embodiment of the invention. Avehicle 11 moves along a selected lane 13B of a roadway 13. The vehiclecarries or has attached thereto a location determination (LD) signalantenna and associated LD signal receiver 16 that receive LD signalsfrom two or more, preferably four or more, satellite-based LD signalsources 19-1, 19-2, 19-3, 19-4. The LD signal sources 19-j (j=1, 2, 3,4) may be part of an LD system such as GPS, GLONASS, LEO (low earthorbit) or other similar LD system that provides timed,frequency-distinguishable and/or coded signals, transmitted from aplurality of satellites whose locations are known and received andprocessed to determine the present location of the LD antenna 15. Threeor more reference LD stations 21-1, 21-2, 21-3, 21-4, whose locationsare known with high accuracy, are located within a wide area or region Rof diameter d at least 50-100 km and also receive and process the LDsignals from the LD signal sources 19-j. Preferably d is in the range50-5000 km. A roadway information module 25 provides local lanedescriptions.

Each LD signal received at a reference station antenna 23-i (i=1, 2, 3,4) is measured to estimate a pseudorange PR(t;i;j;est) from the LDsignal source (j) to the receiving antenna at the reference station. Thereference station 23-i also is provided, or computes, a theoreticallycorrect pseudorange PR(t;i;j;theo) from the LD signal source (j) to thereceiving antenna (i) at the reference station and subtracts theestimated pseudorange. The difference

PRC(t;i;j)=PR(t;i;j;theo)−PR(t;i,j;est)  (1)

represents a pseudorange correction for the LD signal transmitted at theLD signal source 19-j and received at the reference station 21-i. Eachof the network of LD reference stations 21-i computes, or providesinformation to compute, the associated pseudorange correction functionPRC(t;i,j), and these correction functions are provided for an LD masterstation 21, which may but need not coincide with one of the LD referencestations 21-i.

Optionally, the master LD station 21 determines and removes differencesbetween the satellite clocks in order to synchronize these clocks, as ina wide area DGPS correction system described by Enge et al in U.S. Pat.No. 5,621,646. The Enge et al patent is incorporated by referenceherein. In another approach, “Multi-Site Real-Time DGPS System UsingStarfix Link: Operational Results,” described by D. Lapucha and M. Huff,Proceedings of Fifth International Technical Meeting of the SatelliteDivision of the Institute of Navigation, Albuquerque, September 1992, alocal reference station combines DGPS correction information for eachvisible satellite and broadcasts this local area correction informationfor use by local mobile stations.

In another approach, “GPS Wide Area Augmentation System (WAAS) Test BedResults,” by F. Haas, M. Lage and S Kalinowski, Proceedings of theAnnual Meeting of the Institute of Navigation, Colorado Springs, June1994, pseudorange correction information for each in-view satellite isdetermined by each subsidiary reference station and sent to a masterreference station. The master reference station estimates and removesclock differences between the reference stations, now all referenced toa common clock, and forms an average of the pseudorange corrections fora common, in-view satellite for each subsidiary reference station. Theseaveraged pseudorange corrections are then transmitted for use by eachmobile station.

As part of the invention, the master station 21 optionally transmitsclock corrections and ephemeris corrections, or pseudorange or other LDcorrections, that are received by an LD correction signal receiver 18,carried on the vehicle 11, for subsequent use in correcting LDmeasurements over a wide area or region R.

If the LD signal antenna 15 is sufficiently close to one of thereference stations 23-i′, the LD signal receiver 16 can monitor thepseudorange corrections PRC(t;i′;j) applicable at that reference stationand can add these corrections to its own pseudorange measurements,PR(t;LD;j), to obtain estimates of corrected pseudorange measurements

PR(t;LD,j)_(corr,1) =PR(t;LD,j)+PRC(t;i′;j)  (2)

for the LD antenna 15 and use these corrected pseudorange measurementcorrections, referred to as DGPS signals, in Eq. (2) to obtain moreaccurate location coordinates for the LD antenna 15.

Alternatively, if the LD signal antenna 15 is not close to a referencestation, the LD signal receiver 16 may: (1) estimate its own uncorrectedlocation coordinates; (2) use the transmitted pseudorange correctionsfor two or more LD reference stations 21-i1 and 21-i2 that serve theregion R, to estimate its own pseudorange corrections PRC(t;LD;j) fromits estimated location relative to the known locations of the referencestations, 21-i1 and 21-i2, using LD correction signals received at an LDcorrection signal receiver 18; (3) estimate corrected pseudorangemeasurements for the LD antenna 15; and (4) use these correctedpseudorange measurements in Eq. (2) to obtain more accurate locationcoordinates for the LD antenna 15. Code phase pseudorange measurements,if suitably corrected and modified to remove ionospheric propagationtime delay, tropospheric propagation time delay, receiver clock noiseand the presence of multipath signals at the receiver, can allowestimation of LD signal antenna location coordinates that are accurateto within an estimated 10-50 cm., and often to within 10-25 cm.

However, one problem is communication of the pseudorange correctioninformation from the LD reference stations 21-i or from the LD masterstation 21 to any LD signal receiver 16 within a wide area or region R,of the order of a 100 to 5000 km in diameter. One suitablecommunications approach is the Satellite Digital Audio Radio Service(SDARS), which is presently being developed to provide entertainment,weather information, one-way communication and similar signals for avehicle. SDARS will operate in the S-band at 2.320-2.345 GHz. Outsidethe U.S., World Space operates similar communication channels within theL-band at 1.452-1.492 MHz. Presently, each of two companies, SatelliteCD Radio, Inc. (SCDR) and American Mobile Radio Corporation (AMRC), hasan eight-year FCC license to use a band of width 12.5 MHz within theS-band in the U.S. to provide programming and communication for fixed,mobile and portable radios.

In one format, 3 spot beams each use TDMA to carry 96 prime ratechannels with a transmission rate of 16 kbps. These prime rate channelsare combinable to carry broadcast channels of between 16 and 128 kbps;and the audio service components within the broadcast channels areencoded using MPEG layer 3. AMRC will initially provide SDARS servicethrough two or three geosynchronous satellites, each with transmissionpower of up to 9.5 kilowatts.

One or both SDARS licensees plans to deploy terrestrial repeaters or“gap-fillers” to reach urban canyons and other hard-to-reach localregions. According to the terms of the licenses: (1) no programming canbe originated in a gap-filler region, other than from the authorizedSDARS satellites; (2) a terrestrial gap-filler cannot be used to extendSDARS coverage outside the satellites' authorized service areas; and (3)a terrestrial gap-filler can be implemented in a given region only afterobtaining FCC authorization, which will require an adequate showing that(i) the repeating transmitter is located a sufficient distance from theMexican and Canadian borders or will use a previously approved adjacentcountry co-frequency system of communication and (ii) the repeatingtransmitter will comply with Section 17.4 of the FCC rules and Sections1.1301-1.1319 of the FCC's environmental rules. It is likely that theSDARS will be offered on a subscription basis with a small monthlyservice fee, not as a non-subscription, advertiser-supported service.

Another suitable communications approach is use of an FM subcarriersignal to transmit the required LD correction information, at aninformation transfer rate in the range 300-9600 kbps, to a subscribervehicle. An FM subcarrier signal may have an associated frequency ofabout f_(c)±19 kHz, where f_(c) is a selected FM carrier frequency thatlies in the range 88-108 MHz. Alternatively, a higher order displacementfrom the carrier frequency (e.g., f_(c)±38 kHz or f_(c)±57 kHz) may beused. The sources of these FM subcarrier signals may be a plurality ofFM broadcasting stations located in or near a region where a vehicleoperates. In this event, the subcarrier signals are obtained byfiltering the total FM signals (carrier signal plus message signal plussubcarrier signal) to remove all but a subcarrier signal of a chosenfrequency. Data transfer rate is about 300-9600 kbps. Because thecarrier signal frequency used is relatively high, communication using anFM subcarrier signal may be limited to approximately line-of-sighttransmissions, which are generally of the order of 20-60 miles (32-96km).

A third suitable communications approach is the recently disclosed SkyStation system, for which information is available on the Internet athttp://www.skystation.com/faq.html. The Sky Station is a network of asmany as 250 lighter-than-air vehicles (e.g., dirigibles), each having atransmitter or transceiver held in position at about 70,000 feet (about21 km) elevation over a major metropolitan area. A large metropolitanarea, such as London or Tokyo or Mexico City may have severallighter-than-air vehicles servicing the region. Eachtransmitter/transceiver provides 2-10 Mbps broadband, low latencycommunications service covers an area of about 7,500 miles² (about19,000 km²). The downlink and uplink bands used for this purpose will be47.2-47.5 GHz and 47.9-48.2 GHz, respectively. Sky Station services willinclude Internet browsing, and hosting, provision of television-Internetaccess, full motion video, video conferencing, local and long distancetelephony, on-line remote monitoring and security monitoring. The SkyStation system will become available in the year 2,000.

A fourth suitable communications approach, known as Private Radio,operates in a lower band (450-472 MHz) and is available on aseize-and-use basis. Where channels of 12.5-25 kHz width are used here,information transfer rates in the range 300-9600 kbps, and sometimeshigher, are available. Any of the four communications systems discussedin the preceding paragraphs, or any similar system, can be used tocommunicate LD signal correction information to an LD signal receiver ona vehicle over a wide area or region R.

Where LD signals from 8 satellites or other LD signal sources are to becorrected, at a rate such as once every 0.6-2 sec, an LD correctionsignal transfer rate of 300-1200 bps for each source is suitable fornormal intervals when LD signal source location data are not changingrapidly. When LD signal source location data are changing rapidly, forexample, during an ephemeris data changeover period that can occur everytwo hours in GPS, the LD correction signal transfer rate may need to beincreased, to 2400 bps or more per source (19,200 bps for eightsources).

FIG. 1 also illustrates a second embodiment of the invention, whereinone or more roadway segments is mapped using the received LD signals andLD correction signals and a mobile vehicle 11. In this embodiment, thevehicle 11 moves along a roadway segment, such as the lane 13B, so thatits LD signal antenna 15 or some other selected location on the vehicleis displaced from a selected lane boundary, such as 13B-1 or 13B-2, by aselected, approximately constant, horizontal displacement distance oroffset Δh, which may be zero. The LD signal receiver 16 (1) receives LDsignals and LD correction signals as the vehicle 11 moves along theroadway 13, (2) determines a corrected present location of the LDantenna 16 as the vehicle moves and (3) stores the present locationinformation in a memory module, optionally subtracting the offset Δh toprovide a reasonably accurate estimate of the location coordinates at asequence of locations along the selected lane boundary. Proceeding inthis manner, all or a selected fraction of the boundary lanes for aselected segment of a roadway 13 can be mapped and stored for future usein guiding a vehicle along an arbitrary lane on the roadway segment. Thememory module containing the boundary lane location coordinates is thenoptionally downloaded to a central database that will subsequentlyprovide this roadway information for a subscriber vehicle.

FIG. 2 illustrates one approach to broadcast of signals using the SDARSsystem. One or more signal sources (entertainment, news, weather,location correction information, etc.) provide uploadable SDARS programsand other uploaded information to an uplink facility 33, which formatsand transmits this information to an SDARS signal-receiving antenna andreceiver 35 on a selected SDARS satellite 37. The SDARS receiver 35converts the carrier to an S-band (or L-band) carrier, if this has notalready been done, and downloads or otherwise transmits the previouslyuploaded information to one or more subscriber vehicles or other users39. Here, the vehicle 39 is shown as a land vehicle moving on in aselected lane 41B on a roadway 41; but the vehicle 39 may alternativelybe a water vehicle moving along a waterway, as illustrated in FIG. 5.

The vehicle 39 in FIG. 2 carries an LD signal antenna 45 (which servesas surrogate for the user location) and associated LD signal receiver46. The vehicle 39 also carries an SDARS signal antenna and receiver 43,which is connected to or may be a part of the LD receiver 46, thatreceives LD correction information. The SDARS receiver 43 (1) receivesthe downloaded SDARS programming from the SDARS antenna, (2) separatesthe LD correction information from the remainder of the received (audio)signals, (3) selects which LD signals are to be used in determining thelocation of the LD antenna 45, (4) applies the LD correction signals tocorrect the selected LD signals, and (5) uses the corrected LD signalsto determine the present location of the LD signal antenna 45, and ofthe vehicle 39, with an inaccuracy of at most 10-50 cm, and preferablyat most 10-25 cm. In step (2), the LD correction information may beidentified, for example, by header information contained in the SDARSdigital signal. The LD correction information is then processed by oneor more processes for subsequent use by an LD signal receiver, and theremainder of the SDARS signals are subjected to other processes beforepresentation to a vehicle occupant as audio or other signals.

The vehicle 39 estimates and displays its present location relative to apair of spaced apart linear or curvilinear line segments, 41B-1 and41B-2, that indicate the boundaries of a selected roadway lane 41B, asillustrated in FIG. 3. Coordinates for the lane boundary line segments,41B-1 and 41B-2, indicating the boundaries of the selected lane 41B, mayreside in a roadway information database in the LD receiver 46 or may bedownloaded upon demand from a nearby roadway information database 47that provides boundary lane location coordinates for user-selectedsegments of a roadway.

Optionally, the LD signal receiver 46 also compares its present locationcoordinates, (x_(u)(t),y_(u)(t),z_(u)(t)), with location coordinates,(x_(u)(t−Δt),y_(u)(t−Δt),z_(u)(t−Δt)), taken at a preceding time anddisplays one or more difference measures, such as,

v _(x)(t)={x _(u)(t)−x _(u)(t−Δt)}/Δt,  (3A)

v _(y)(t)={y _(u)(t)−y _(u)(t−Δt)}/Δt,  (3B)

v _(z)(t)={z _(u)(t)−z _(u)(t−Δt)}/Δt,  (3C)

of how quickly the vehicle 39 is approaching one or the other of thelane boundaries 41B-1 or 41B-2. When the user 39 location actuallycrosses into an adjacent lane, such as 41A or 41C in FIG. 3, the LDreceiver promptly substitutes new line segments as lane boundaries forthe new selected lane. If one or more of the velocity components, suchas v_(y)(t), as computed in Eq. (3B), exceeds a selected thresholdvalue, v_(y,thr), the LD receiver 46 in FIG. 2 may generate and issue ortransmit a visual, audible and/or alphanumeric alarm signal to alertsomeone—either a vehicle occupant or another person or computer—that thevehicle 39 is approaching a selected lane boundary at greater than apermissible velocity. The system may also display, in a graphical formatand/or an alphanumeric format, a computed velocity of approach of thevehicle 39 toward a selected lane boundary.

A Wide Area LD correction system can also be used to monitor theapproximate separation distance Δs between a vehicle and the nearestlane boundary. If the vehicle is too close to this lane boundary (e.g.,within 20-50 cm or within 50-100 cm), the system can generate an audibleor visual alarm.

FIGS. 3 and 4 schematically illustrate one method for determination ofvelocity of vehicle approach to a nearby lane boundary line B1—B1. Thisboundary line is locally approximately as a straight line segment L1—L1,which is oriented at an angle θ_(B) relative to the x-axis of a local,two-dimensional Cartesian coordinate system (x,y). In this coordinatesystem, the line segment L1—L1 has a unit length perpendicular or normalvector π_(B), which is oriented at an angle −(θ_(B)+π/2) relative to thex-axis. The vehicle 39 is moving with a velocity vector v and angleθ_(V) relative to the x-axis, and is approaching the line segment L1—L1(or lane boundary B1—B1) at a rate of

v·π _(B) =|v| sin(θ_(V)−θ_(B)).  (4)

The magnitude |v·π_(B)| is compared with a selected threshold rate ofapproach v_(thr) for audible or visual alarm signal purposes.

A third embodiment is useful to determine the location of a marine orwater vehicle 51 (FIG. 5) relative to a (usually non-visible) boundary Bfor travel by the vehicle on a navigable waterway 52. Information on theboundary B is downloaded from a roadway information database, whichdatabase may be on board the vehicle or may be located apart from thevehicle 51. The boundary information may, for example, be (1) a curvethat represents closest safe approach to a shoal or shoreline, based onlocal water depth, or (2) a boundary between two different legaljurisdictions, such as between Canada and the United States in the SaintLawrence River or (3) a (preferably continuous) curve defined for otherpurposes. Here, an operator of the water vehicle 51 will seldom be ableto determine visually an appropriate boundary curve.

The water vehicle 51 carries an LD signal antenna 53, an LD signalreceiver and database 54, an LD correction signal antenna 55 and an LDcorrection signal receiver 56 (which may be part of the LD receiver 54)that receive LD signals and correction signals and accurately determinethe vehicle location (and, optionally, the vehicle velocity vector). LDsignals are received from two or more LD signal sources 57-1, 57-2,57-3, 57-4, at the LD receiver 54 and at several LD reference stations58-1, 58-2, 58-3 that serve a Wide Area LD correction system. The LDreference stations 58-1, 58-2, 58-3 and/or LD master reference station58 provide LD correction information for the LD receiver 54. Optionally,the LD receiver 54 receives waterway boundary lane information from awaterway information database 59 that is spaced apart from the vehicle51; or the LD receiver may receive such information to an on-boardwaterway information database.

The present location (and, optionally, the present velocity vector) ofthe vehicle 51 is compared with a geometric description of the boundaryB contained in the database, and an alarm signal is optionally issued if(i) the vehicle is either too close to, or has crossed over, a laneboundary B or (ii) the vehicle is approaching the lane boundary B at agreater-than-threshold velocity.

FIG. 6 schematically illustrates apparatus 61, carried on or installedin a vehicle 60, suitable for practicing the invention. The apparatus 61includes an LD signal antenna 63 and associated LD signal receiver 65that receive and process (uncorrected) LD signals from a plurality of LDsignal sources, such as GPS or GLONASS or LEO satellites. The apparatusalso includes a radiowave antenna 67 and associated radiowave receiver69 that receives LD signal correction information and (optionally) othersignals containing entertainment, news, weather information, one-wayand/or two-way communication and similar signals (collectively referredto herein as “supplemental signal information”). The radiowave receiver69 includes an LD signal filter 71, preferably implemented in software,that examines an incoming digital signal (e.g., the header and/or footerof an incoming signal) and separates LD signal correction informationfrom other supplemental signal information. Optionally, the LD filter 71directs the LD correction signal information to an LD signal port 73that delivers this LD signal information to the LD signal receiver 65for appropriate processing. The supplemental signal information isdelivered by the LD filter to a supplemental processing module 75 (e.g.,an audio signal processor) for delivery to a vehicle occupant in anotherformat.

The radiowave receiver 69, LD signal filter 71, LD signal port 73 andsupplemental processor 75 are optionally part of the LD signal receiver65. The LD receiver 65 uses the LD signal information and the LD signalcorrection information to determine the location of the vehicle relativea lane of a roadway on which the vehicle 60 travels, with an associatedinaccuracy that is no more than 10-50 cm, preferably no more than 10-25cm.

The LD signal receiver 65 is connected to a roadway information database77 that contains relevant information on each roadway or waterway in agiven region, such as number of lanes, lanes allocated to vehicle travelin each direction, width of each lane and geometric description of eachlane boundary. The LD receiver 65 determines the present location of thevehicle 60, locates the vehicle within a likely lane of a roadway orwaterway, and optionally displays the vehicle location within the lane,using a graphical or alphanumeric display 79. Optionally, the apparatusalso has a visual or audible alarm signal mechanism 81 that is connectedto and is activated by the LD receiver 65 if the vehicle appears to bemoving into a lane that is allocated to vehicle travel in an oppositedirection. Power for the other components of the apparatus 60 isprovided by a power sources 83.

An example of a Wide Area LD correction system, not including the meansto transfer the LD correction information to a mobile user fornavigation or tracking within a vehicle lane, is the Omnistar system inNorth America, which presently includes 11 reference station sites, atthe following locations:

San Diego, Calif.

Redding, Calif.

Everett, Wash.

Duluth, Minn.

Long Island, N.Y.

Fayetteville, S.C.

Melbourne, Fla.

Pensacola, Fla.

Houston, Tex.

Mercedes, Tex.

Ciudad del Carmen (Yucatan Peninsula)

With the exception of the distance between the Houston and Mercedessites and the distance between the Melbourne and Pensacola sites, thedistance between any other pair of sites is several hundred km; and thedistance between the Everett and Fayetteville sites is about 4,000 km.Thus, a vehicle placed anywhere in the continental U.S., includingAlaska, will be several hundred km to several thousand km from at leasttwo reference station sites in the Omnistar system.

The Omnistar system is similar to the GPS system discussed by Haas, Lageand Kalinowski, op cit, in which a central station (at Houston forOmnistar) receives and processes differential GPS corrections from eachof a plurality of reference stations and provides an averaged DGPScorrection for each visible satellite. This set of 10 reference stationsand a master reference station provides reasonably good LD correctioncoverage for the 48 contiguous states, most of southern and westernCanada, the eastern half of Alaska and substantially all of Mexico,although the 11 choices of site locations were not optimized to providethis coverage.

In one informal test of the accuracy of the Omnistar system, computedlocations in the vicinity of one or another of the reference stationshad associated inaccuracies of the order of 20-40 cm, which is withinthe desired range of inaccuracies required for a Wide Area LD correctionsystem.

A Wide Area LD correction system with only a few reference stations canprovide adequate coverage of the 48 contiguous states, and of Alaska,Canada and Mexico if desired, with a maximum inaccuracy (10-50 cm or,preferably, 10-25 cm) that is sufficient for tracking vehicle locationwithin a lane. One important benefit of use of a Wide Area LD system,with relatively few reference stations, for vehicle tracking is that thetotal information transfer rate for LD correction information for allthe reference stations is relatively small, an estimated 9.6-19.2 kbps,and can be provided by several different communication systems, such asSDARS, an FM subcarrier system, Sky Station and Private Radio.

By contrast, a real time kinematic (RTK) location determination systemwill provide corrected location coordinates with smaller inaccuracies(1-4 cm in some situations), but only over a small region, with anestimated maximum radius of about 40 km. It is estimated that more than750 RTK reference stations would be required to provide adequatecoverage of the 48 contiguous states, and this pattern would provide nocoverage of Alaska and would cover only a small fraction of southernCanada and northern Mexico. Transfer of LD correction information for anetwork of this size would require an estimated 7.2-14.4 Mbps, and onlya few communication systems today can provide such a high transfer rate.

What is claimed is:
 1. A method for vehicle navigation on a selectedlane on a vehicle path, the method comprising the steps of: obtainingcoordinates for a boundary line segment that helps define said selectedlane on a selected path on which a vehicle travels; receiving locationdetermination (LD) signals and LD correction signals that allowestimation and correction of the present location of the vehicle,relative to the selected lane, with an inaccuracy that is no more thanabout 50 cm, where the LD correction signals are provided by at leastthree spaced apart LD correction signal sources, with at least two ofthe LD correction signals being produced by LD correction signal sourcesthat are at least a selected distance d from the vehicle, where d is atleast 50 km, said step of receiving location determination (LD) signalsand LD correction signals further comprising receiving said LDcorrection signals as part of a composite signal that also contains atleast one signal that is unrelated to said LD correction signals and tosaid LD signals; and separating said LD correction signals from the atleast one signal that is unrelated to said LD correction signals and tosaid LD signals; and determining and displaying, in at least one ofgraphical form and alphanumeric form, the present location of thevehicle relative to the boundary line segment.
 2. The method of claim 1,further comprising the step of selecting said distance d to be at least100 km.
 3. The method of claim 1, further comprising the step ofselecting said distance d to be at least 500 km.
 4. The method of claim1, further comprising the step of selecting said distance d to be atleast 1000 km.
 5. The method of claim 1, further comprising the step ofdetermining a velocity in a selected direction with which said vehicleapproaches at said boundary line segment for said selected lane.
 6. Themethod of claim 5, further comprising the step of providing an audibleor visual alarm signal if said velocity with which said vehicleapproaches said boundary line segment exceeds a selected thresholdvelocity value.
 7. The method of claim 5, further comprising the step ofdisplaying, in at least one of graphical form and alphanumeric form,said velocity with which said vehicle approaches said boundary linesegment.
 8. The method of claim 1, further comprising the step ofproviding an audible or visual alarm if said vehicle is closer than aselected threshold separation distance from said boundary line segment.9. The method of claim 1, further comprising the step of selecting saidvehicle path to be a roadway and selecting said vehicle to be a landvehicle.
 10. The method of claim 1, further comprising the step ofselecting said vehicle path to be a waterway and selecting said vehicleto be a water vehicle.
 11. The method of claim 1, wherein said step ofobtaining said coordinates for said boundary line segment comprises thestep of receiving said coordinates from a roadway information databasethat is spaced apart from said vehicle.
 12. The method of claim 1,wherein said step of obtaining said coordinates for said boundary linesegment comprises the step of receiving said coordinates from a roadwayinformation database that is on said vehicle.
 13. The method of claim 1,wherein said step of receiving said LD corrections signals comprisesreceiving said LD correction signals from a communications system drawnfrom a group of communications systems consisting of Satellite DigitalAudio Radio Service, FM subcarrier service, Sky Station and PrivateRadio.
 14. A system for vehicle navigation on a selected lane on aselected path, the system comprising a computer that is programmed to:obtain coordinates for a least one boundary line segment that helpsdefine said selected lane on a path on which a vehicle travels; receivelocation determination (LD) signals and LD correction signals that allowestimation of the present location of the vehicle, relative to theselected lane with an inaccuracy that is no more than about 50 cm, withat least two of the LD correction signals being produced by LDcorrection signal sources that are at least a selected distance d fromthe vehicle, where d is at least 50 km; determine and display, in atleast one of graphical form and alphanumeric form, the present locationof the vehicle relative to the boundary line segment; receive said LDcorrection signals as part of a composite signal that also contains atleast one signal that is unrelated to said LD correction signals and tosaid LD signals; and separate said LD correction signals from the atleast one signal that is unrelated to said LD correction signals and tosaid LD signals.
 15. The system of claim 14, wherein said selecteddistance d is at least 100 km.
 16. The system of claim 14, wherein saidselected distance d is at least 500 km.
 17. The system of claim 14,wherein said selected distance d is at least 1000 km.
 18. The system ofclaim 14, wherein said computer is further programmed to determine avelocity in a selected direction with which said vehicle approaches saidboundary line segment for said selected lane.
 19. The system of claim18, wherein said computer is further programmed to provide an alarmsignal if said velocity with which said vehicle approaches said boundaryline segment exceeds a selected threshold velocity value.
 20. The systemof claim 14, wherein said computer is further programmed to display, inat least one of graphical form and alphanumeric form, said velocity withwhich said vehicle approaches said at least one of said boundary linesegments.
 21. The system of claim 14, wherein said computer is furtherprogrammed to provide an audible or visual alarm if said vehicle iscloser than a selected threshold separation distance from said boundaryline segment.
 22. The system of claim 14, wherein said vehicle path is aroadway and said vehicle is a land vehicle.
 23. The system of claim 14,wherein said vehicle path is a waterway and said vehicle is a watervehicle.
 24. The system of claim 14, wherein said computer is furtherprogrammed to receive said coordinates for said boundary line segmentfrom a roadway information database that is spaced apart from saidvehicle.
 25. The system of claim 14, wherein said computer is furtherprogrammed to obtain said coordinates for said boundary line segmentfrom a roadway information database that is on said vehicle.
 26. Thesystem of claim 14, wherein said LD correction signals are received froma communications system drawn from a group of systems consisting ofSatellite Digital Audio Radio Service, FM subcarrier service, SkyStation and Private Radio.